Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$85.88	6.686%	$91.6219	$91.62	$91.60	$91.60
Purchase #2	$200.91	6.443%	$213.8546	$213.85	$213.85	$213.90
Purchase #3	$69.48	13.121%	$78.5965	$78.60	$78.60	$78.60
Purchase #4	$232.49	7.763%	$250.5382	$250.54	$250.55	$250.50
Purchase #5	$162.98	10.365%	$179.8729	$179.87	$179.85	$179.90
Purchase #6	$164.48	12.527%	$185.0844	$185.08	$185.10	$185.10
Purchase #7	$218.47	6.339%	$232.3188	$232.32	$232.30	$232.30
7 purchase totals =	$1,134.69		$1,231.8873	$1,231.88	$1,231.85	$1,231.90